echo.z80

;***************************************************************************
;  PROGRAM:         UART  Echo Test Program
;  PURPOSE:         Key typed on PC will display
;  ASSEMBLER:       TASM 3.2
;  LICENCE:         The MIT Licence
;  AUTHOR :         MCook
;  CREATE DATE :    15 Mar 15
;***************************************************************************

UART0:       .EQU    00H            ; DATA IN/OUT
UART1:       .EQU    01H            ; CHECK RX
UART2:       .EQU    02H            ; INTERRUPTS
UART3:       .EQU    03H            ; LINE CONTROL
UART4:       .EQU    04H            ; MODEM CONTROL
UART5:       .EQU    05H            ; LINE STATUS
UART6:       .EQU    06H            ; MODEM STATUS
UART7:       .EQU    07H            ; SCRATCH REG.

.ORG 00H

;***************************************************************************
;INIT_UART
;Function: Initialize the UART to BAUD Rate 9600 (1.8432 MHz clock input)
;DLAB A2 A1 A0 Register
;0    0  0  0  Receiver Buffer (read),
;              Transmitter Holding
;              Register (write)
;0    0  0  1  Interrupt Enable
;X    0  1  0  Interrupt Identification (read)
;X    0  1  0  FIFO Control (write)
;X    0  1  1  Line Control
;X    1  0  0  MODEM Control
;X    1  0  1  Line Status
;X    1  1  0  MODEM Status
;X    1  1  1  Scratch
;1    0  0  0  Divisor Latch
;              (least significant byte)
;1    0  0  1  Divisor Latch
;              (most significant byte)
;***************************************************************************

INIT_UART:
            LD     A,80H            ; Mask to Set DLAB Flag
            OUT    (UART3),A
            LD     A,12             ; Divisor = 12 @ 9600bps w/ 1.8432 Mhz
            OUT    (UART0),A        ; Set BAUD rate to 9600
            LD     A,00
            OUT    (UART1),A        ; Set BAUD rate to 9600
            LD     A,03H
            OUT    (UART3),A        ; Set 8-bit data, 1 stop bit, reset DLAB Flag


MAIN:
            LD      A,00H

;***************************************************************************
;GET_CHAR_UART
;Function: Get current character from UART place in Accumulator
;***************************************************************************

GET_CHAR_UART:
            IN      A,(UART5)       ; Get the line status register's contents
            BIT     0,A             ; Test BIT 0, it will be set if the UART is ready to receive
            JP      Z,GET_CHAR_UART

            IN      A,(UART0)       ; Get character from the UART
            LD      B,A             ; Store character into B Register

;***************************************************************************
;SEND_CHAR_UART
;Function: Send current character in Accumulator to UART
;***************************************************************************

SEND_CHAR_UART:
            IN      A,(UART5)       ; Get the line status register's contents
            BIT     5,A             ; Test BIT 5, it will be set if the UART is ready to send
            JP      Z,SEND_CHAR_UART

            LD      A,B             ; Get character from B Register obtained earlier
            OUT     (UART0),A       ; Send character through the UART

    JP      MAIN

.END